Tin salts of partially esterified vinyl monomer-maleic anhydride copolymers

ABSTRACT

NOVEL TIN SALTS OF PARTIAL ESTERS OF VINYL MONOMERMALEIC ANHYDRIDE POLYMERS (E.G. STYRENE-MALEIC ANHYDRIDE POLYMERS), ESTERIFIED WITH A THIOALCOHOL OR A HYDROXYTHIOETHER ARE FORMED BY COMBINATION OF THE AMMONIUM SALT OF SAID THIOESTER AND STANNOUS CHLORIDE. VINYL HALIDE POLYMERS ARE STABILIZED BY INCORPORATION OF SMALL AMOUNTS OF THESE TIN SALTS.

United States Patent 3 640 97s TIN SALTS 0F PARIIALLY ESTERIFIED VINYLMONOMER-MALEIC ANHYDRIDE COPOLYMERS Robert R. Chambers, Scarsdale, N.Y.,Henry V. Isaacson,

US. Cl. 260-785 T 5 Claims ABSTRACT OF THE DISCLOSURE Novel tin salts ofpartial esters of vinyl monomermaleic anhydride polymers, (e.g.styrene-maleic anhydride polymers), esterified with a thioalcohol or ahydroxythioether are formed by combination of the ammonium salt of saidthioester and stannous chloride. Vinyl halide polymers are stabilized byincorporation of small amounts of these tin salts.

This is a division of application Ser. No. 734,202, filed June 4, 1968,which is a continuation-in-part of our application Ser. No. 607,150,filed Jan. 4', '1967, now US. Pat. No. 3,472,772.

The present invention relates to certain metal salts, particularly thetin salts of thioalcohol-esterified and hydroxythioether esterifiedvinyl monomer maleic anhydride polymers, and to vinyl halide polymersstabilized with small amounts of these tin salts. It has now been foundthat certain metal salts, e.g., the tin salts of these esters, exhibitstabilizing effects in, for instance, polyvinyl chloride compositions,e.g., PVC plastisols.

Vinyl halide resins, in general, are well known to the art and theirdesirable properties as components of solid plastic compositions ofvarious types have been recognized. It is also known that vinyl halideresins are sensitive to both heat and light as manifested bydiscoloration. By way of illustration, in the compounding and processingof these resins into molded and extruded articles such as syntheticfibers and films, or as constituents of coating compositions, it isusually necessary to subject the resins to elevated temperatures. Undersuch conditions a tendency of the resins toward progressive yellowing ordarkening is commonly encountered. Consequently, it has become thepractice to incorporate small amounts of stabilizing materials into theresins to retard or inhibit this degradation or discoloration. Manystabilizers have been suggested for this purpose, the most prominent ofwhich are the organo-metallic compounds, particularly those containingtin or lead, such as dibutyl tin, dibasic lead phosphate, dioctyl tinmaleate, lead stearate, etc. Unfortunately, however, many of thesestabilizers have not been found entirely satisfactory for one reason oranother. Hence, there exists a continuing demand for new stabilizers.

The esterified polymers of the present invention are prepared bypartially esterifying a vinyl monomer-maleic anhydride polymer with acompound having the general formula:

wherein R is a hydrocarbon radical of about 1 to 20, preferably about 1to 12, carbon atoms and R is a radical selected from the groupconsisting of hydrogen and alkylols of about 1 to 24, preferably about 1to 12 carbon atoms. Thus, suitable esterifying compounds arethioalcohols, known also as thiols and mercaptans, and hy- 3,640,973Patented Feb. 8, 1972 droxythioethers, known also as thioetheralcohols.Preferably, R is alkyl. Illustrative esterifying compounds include, forexample, methyl mercaptan, ethyl mercaptan, isooctyl mercaptan,ethylthioethanol, etc.

The reaction between the polymer and the esterifying compound takesplace at the dicarboxylic anhydride sites of the polymer to formthioester or thioetherester linkages. Thus, the reaction of one mole ofthioalcohol with sutficient vinyl monomer-maleic anhydride polymer toprovide one mole of maleic anhydride unit, would yield a polymericproduct having the following half-thioester of the maleic acid unit:

The percent, or extent of esterification of the polymer is a factor indetermining the utility of the sulfur-containing, esterified polymers ofthe invention. By percent esterification is meant the overall percentageof total potential carboxyl groups on the polymer chains that are in theform of the thioester group, i.e.

i O-SR or in the form of the thioetherester group, i.e.

SR, R representing the radical defined above and R representing theresidue of the alkylol radicals of a hydroxythioether. Potentialcarboxyl groups include carboxyl groups as such and groups capable ofyielding the carboxyl group by hydrolysis and having the formula:

II COX where X is hydrogen, hydrocarbyl, metal or carbon (e.g., as inthe case of the anhydride). Thus, for instance, where 25% of the totalpotential carboxyl groups of the vinyl monomer-maleic anhydride polymerare esterified (25% esterification), the product is a polymer having 50%esterification based on half-esterification. The higher the percentageof esterification, the lower the solubility of the polymer in aqueous,alkaline media and the greater the organic solvent, e.g., hydrocarbon,solubility. The present invention contemplates polymers which areesterified with the above sulfur-containing compounds in the range ofabout 5 to 95, preferably about 25 to percent. Where it is desired torender the esterified polymer water-soluble, the percent esterificationis also important from the standpoint of leaving enough unreactedcarboxyl groups to permit sufficient alkali metal or ammonium saltformation to impart water solubility. Further, it may be desired toallow sufficient carboxyl groups to remain free for subsequentcross-linking reactions.

The esterification reactions can be conducted by known methods. Often,temperatures of about 50 C. to 200 C., preferably about to C., can beemployed. The reaction may be conducted in bulk or in the presence ofsuitable solvents such as, for example, xylene, toluene, or an excess ofthe esterifying sulfur-containing compound. The reaction proceedswithout the additional presence of catalyst; however, such may beemployed, if desired, and as suitable catalysts may be mentioned lithiumacetate and sodium metsoxide. Reaction times can vary according toreactant proportions, the presence or absence of catalysts and diluents,temperature, pressure, etc. The

main consideration as regards reaction time, however, is the extent ofesterification sought.

The esterified polymers of the present invention are renderedwater-soluble by conversion of unreacted carboxyl groups of thecopolymer to their alkali metal or ammonium salt forms. Preparation ofthe salt can be by known methods such as by the addition of thethioesterified or thioetherified polymer to a hot aqueous solution ofammonium hydroxide. The tin salts are prepared by a subsequent additionof a tin salt, for example tin chloride, to the aqueous solution of theammonium salt.

Similarly, an aqueous solution of the alkali metal salt of the polymerester can be added to at least about stoichiometric amounts of aninorganic or organic salt of tin. Other salts can be used in place oftin chloride, such as water-soluble tin nitrates and acetates. It ispreferred that the tin salt be in aqueous solution on addition of thealkali metal salt solution of the aqueous solution of the copolymer.Addition with continuous stirring provides the novel tin salts of theinvention which are insoluble in the reaction medium and precipitateimmediately out of solution. The tin salts of this invention give acolorless film.

In the tin salt of these esters the amount of tin is often about 10-25%by weight of the ester salt. Enough tin is present so that these estertin salts are essentially water-insoluble even though they are made froma watersoluble ammonium or sodium salt.

The concentration of the tin salts of the copolymerester in thepolyvinylhalide materials, which constitute the major amount of thecomposition of the invention, can vary but in all cases is a minoramount sufficient to stabilize the polyvinylhalide against degradation.Usually the additive concentration in about 0.01% to by Weight,preferably 0.25% to 2%, of the composition.

The polymer with which the sulfur-containing compounds are reacted toform the thioesters or thioetheresters of the present invention is apolymer of maleic anhydride and a polymerizable monovinyl compound of 2to about 12 carbon atoms, these components being present in the polymerin a molar ratio of vinyl monomer to maleic anhydride of about 1:1 to5:1, preferably about 1:1 to 3:1. Suitable vinyl compounds include, forinstance, ethylene, propylene, isobutylene, butylene, pentylene,hexylene, heptylene, octylene, nonylene, decylene, dodecylene, methylvinyl ether, ethyl vinyl ether, butyl vinyl ether, styrene, vinyltoluene, and the like. The preferred vinyl monomer is styrene. Ifdesired, maleic acid can be used instead of maleic anhydride information of the polymer, and the use of the term maleic anhydrideherein and in the claims is intended to include maleic acid.

The polymer contains repeating vinyl monomer and maleic anhydride unitsand, in unesterified form, may have an average molecular weight of about400 to 18,000, preferably about 600 to 15,000. The melting point maygenerally range from about 800 to 300 C., and a by weight solution ofthe polymer in acetone will generally exhibit a viscosity at 30 C. of upto about 2 centistokes, preferably less than about 1 centistoke.

Preparation of the vinyl monomer-maleic anhydride polymer can be byknown methods. A preferred method :is by solution polymerization Wherethe monomers are polymerized in a suitable solvent employing as apolymerization catalyst a free-radical catalyst, such as a peroxide,preferably benzoyl peroxide, dicumyl peroxide, or an alkyl peroxydicarbonate, at a temperature of about 75 to 300 C. or more. Suitablesolvents include the aromatic hydrocarbon solvents, such as cumene,p-cymene, xylene, toluene, etc. Other suitable solvents are the ketones,such as methylethylketone. The preferred manner of carrying out thepolymerization is by what is known as incremental feed addition. By thismethod the monomers and catalyst are first dissolved in a portion of thesolvent in which ,the polymerizatbn is to be conducted and the resultingsolution fed in increments into a reactor containing solvent heated toreaction temperature, usually the reflux temperature of the mixture.

When an aromatic solvent is employed as the solvent for thepolymerization, the formation of the copolymer causes a heterogeneoussystem, the polymer layer being the heavier layer and recoverable bymerely decanting the upper aromatic solvent layer and drying. On theother hand, when a ketone is the solvent, the formed copolymer isusually soluble in the solvent media so that recovery of the productnecessitates a solvent stripping operation.

Typical properties of, for example, styrene maleic anhydride resins fromwhich the tin salts of the thioesters or thioetheresters of the presentinvention can be prepared as follows:

As employed herein, the term vinyl halide resin is meant to includethose resins prepared by the polymerization of a vinyl halide eitheralone, or in conjunction with other ethylenically unsaturatedpolymerizable monomers, such as vinylidene chloride, acrylonitrile,styrene, vinyl esters of aliphatic acids, as for instance vinyl acetate,alkyl esters of monoolefinic acids, as for instance, dialkyl fumerate ormaleate, and the like; and also vinylidene chloride polymer. Themonomers other than the vinyl halide often are of 2 to 10 carbon atomsand preferably are monovinyl structures having an alpha olefin bond. Thesolid vinyl halide resin concerned with here is ordinarily the majorconstituent, preferably at least about 75% of the vinyl halide resin,and is preferably the chloride, although the other halides, such as thebromide and fluoride, are also contemplated. Otherethylenically-unsaturated monomers which can constitute the minorportion of. the vinyl halide resin are often present in an amount up toabout 25% or up to about 10%, more commonly about 5% by weight. Thevinyl halide resins generally have Staudinger molecular weights of about30,000 to 150,000, preferably about 50,000 to 75,000. The invention isof particular merit when applied to vinyl halide resins prepared by thepolymerization of vinyl chloride either alone, or in conjunction withacrylonitrile, vinylidene chloride or both, or with vinyl acetate, andespecially the vinyl chloride-vinyl acetate polymer resins.

If desired, other known stabilizers can be utilized in combination withthe stabilizer of the present invention. It is also to be understoodthat other ingredients commonly added to vinyl halide resin compositionssuch as plasticizers, pigments, dyes, fillers, etc., may also beincorporated into the vinyl halide resins. Among the more popularplasticizers, for instance, are the monomeric ester plasticizersobtained from the reaction of a carboxylic acid and an alcohol having 4to 12 carbon atoms. Examples of suitable plasticizers are dioctylphthalate, di-2-ethylhexylphthalate, isooctyl sebacate, isooctyladipate, and polyester polymers of polyalkanols and polycarboxylicacids.

The following examples. which are to be considered illustrative only andnot limiting, describe the preparation of the novel products andcompositions of the present invention.

EXAMPLE I Into a 500 ml. resin kettle was added a mixture of thestyrene-maleic anhydride polymer grams) identified in Table I as Resin Aand 2-rnethyl-2-heptanethiol,

known synonymously as tert-octylmercaptan, (55 grams). The plastisolswere fused by drawing down a 1 mil The kettle was immersed in an oilbath at 200 C. and film on a glass plate and then placed in acirculating air kept there for five hours with stirring; the resin thusoven at 355 F, The samples were removed from the tmated Was thenPrecipitated in acetone and dried- The oven at 5 minute intervals up to25 minutes. The extent resulting Product was approximately 50%half'thio' of discoloration of the fused film is shown in Table II esterof the styrene-maleic anhydride polymer. The prodwhereby B (with finSalts f Example I) and c (with analyzed: 71-46 Percent Percent dibutyltin dilaurate) showed best results for heat staand 3.05 wt. percent S.bility of resin The ammonium salt was prepared by addition of the TABLEII Test A B C D Stabilizer Dyphos PG Tin salt of thioesters ofstyrenemaleic anhydride polymeiz-.. Dibutyl tin dilaurate" Control; Nostabilizer.

minutes. Good Good Good 00d. 10 minutes do. ..do do Very faintdiscoloration. niinutes Starting discoloration do Faint discolorationDisooloration. minutes. Bad Faint discoloration Bad Bad. minutes doSlight discoloration do Do.

thioester to a warm (50 C.) solution of ammonium 2Q hydroxide. Theammonium salt of the thioester was then To test the eifect of weightpercent of additive staprecipitated in acetone and dried. The analysisof the bilizer on the results, the following runs were made as resultantammonium salt is as follows: 71.96% C; 6.6% shown in the followingtable: H; 3.21% S.

TABLE III Test A2 B2 C2 D2 Polyvinylchlon'de plastisol (Geon 121) 100grams 100 grams. 100 grams"-.. 100 grams. Di-2-ethyl hexyl phthlate 65grams 65 grams 65 grams 65 grams. Tin salt of thioester ofstyrene-maleie anhydride polymer of Example 1.. 0.05 gram. Dibutyl tindilaurate 5 minutes.. Good" d 0. do... Faint ohange Bad.

20 minutes .d0 aint ohange.. Bad Very bad. 25 minutes Discoloring spotd0 do Bad.

Tin salt of the above thioester was prepared as follows: It is claimed:

Thirty-five grams gm.) of the thioester was dis- 1. The tin salt of apartially esterified vinyl monomermaleic anhydride polymer having amolar ratio of vinyl monomer to maleic anhydride of about 1:1 to 5:1 andan solved in a warm dilute solution NH OH. A 10% solution of SnCl (25gm.) in water was then added drop- 40 Wis '10 am Salt Solution, and thetin Salt P unesterified molecular Weight of about 400 to 18,000, saidcipitated out The Salt was then Washed W acetone vinyl monomer having 2to about 12 carbon atoms, whereand dried for 5 days at room temperaturein a vacuum in about 5 to 95 percent f the carboxyl groups in said overq apolymer are esterified with a compound corresponding to Analysis ofthe tin salt of the tert-octylthioester of the formula: styrene-maleicanhydride polymer showed 16.2% Sn.

EXAMPLE II A mixture of the St rene maleic anhydride p y wherein R is ahydrocarbon radical of about 1 to 20 car- (101 grams) identified iiiTable I as Resin A and ethyl 5 11011 atoms d R 18 a monovalent radicalselected from thioethanol g was heated in a resin p with the groupconsisting of hydrogen and alkylols of about 1 agitation at 200 C. forfive hours. After precipitation in to f th t d 1 f 1 1 acetone anddrying, the ammonium salt of the hydroxyz o e 1 6 PO ymer o C almthioetheresterified polymer was prepared by reaction with w erem e vmymonomer y hot, aqueous ammonium hydroxide. The salt analyzed: I E saltof the esterified Polymer of Clam 2 62.29 wt. percent C, 7.07 wt.percent H, and 4.96 wt. per- Wherem R 15 alkylcent S. The tin salt isprepared from the ammonium salt 1 tin Salt of 'E esterified p y of Claim1 in the same manner as Shown i Example I. wherein the molar ratio ofstyrene to malelc anhydride is approximately 1: 1. EXAMPLE HI 60 5. Thetin salt of the esterified polymer of claim 4 The tin salt of thethioester as made in Example I was wherein said polymer is esterifiedwith tert-octylmertested as a stabilizer for the fusion ofpolyvinylchloride captam plastisols (Geon 121) The tin salt of thethioester was References Cited tested against a commercial stabilizerbasic lead phosphate (Dyphos PG), and the commercial di-butyl tin di-UNITED STATES PATENTS laurate. The polyvinylchloride plastisols testedare shown 2,606,891 8/1952 Rowland 260 78'5 be1w the table 2,615,84510/1952 Lippincott et a1. 252--56 TABLE I Test A B 0 D JOSEPH L.SCHOFER, Primary Examiner n 1 i 1 G 12fiilhiliiiiiyitttiiit15182321183,5.--. it it 25% 22 KIGHT AS8180 Exam"DyphosPG(basielead phosphate),g 1 Tin salt of tert-octylthioester 0istyrenemaleic U S.C1 X R anhydride polymer,g 1

Dibutyltmdmmihg 260--45.75, 45.75 K, 899

